Metalloporphyrins spectroscopic properties

Due to the biochemical importance of porphyrine systems their metal complexes have been modeled extensively. Metalloporphyrines are assumed to be planar but there is a relatively high degree of flexibility, and six low energy distortion modes have been described (Figure 3).127 MM with a variety of force fields has been used to compute the structural and dynamic properties,65 66 128-131 and these studies also include information on the orientation of the axial donors.132 133 Reaction dynamics related to the interaction of substrates with the metal site have also been modeled,134-136 and MM has been used to correlate structural and spectroscopic properties (primarily Raman frequencies).137 138... 

Porphyrins are well known for their ligation with various metal centers to form metalloporphyrins. Coordination of the metal ions typically has a dramatic effect on the It delocalization in the molecule. Inherited changes are very obvious in spectroscopic analysis and in their properties. Especially, the electronic spectra of metalloporphyrins are dependent on the identity of the metal ion, axial ligation, oxidation level, and spin state. Typically, metal coordination reduces the number of observed Q bands of porphyrin, indicating the acquisition of higher symmetry of the chromophore relative to the free base. X-ray structural determinations reveal that the bond length of porphyrin changes upon coordination with metal ions [39]. 

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